begin{table}[h]
centering
begin{tabular}{| p{.20textwidth} | p{.80textwidth} |}
hline
foo & bar \ hline
foo & bar \ hline
...
end{tabular}
end{table}

documentclass{article}

usepackage{longtable}
usepackage{lipsum} % just for dummy text- not needed for a longtable

begin{document}
lipsum[1]
lipsum[1]
lipsum[1]

%begin{table}[h]
%centering
begin{longtable}{| p{.20textwidth} | p{.80textwidth} |}
hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
foo & bar \ hline
caption{Your caption here} % needs to go inside longtable environment
label{tab:myfirstlongtable}
end{longtable}
%end{table}

Table ref{tab:myfirstlongtable} shows my first longtable.
end{document}